Detailed explanation of PHP bubble algorithm (recursive implementation), bubble recursion

Detailed explanation of PHP bubble algorithm (recursive implementation), bubble recursion_PHP tutorial

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Release： 2016-07-13 10:14:29

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Detailed explanation of PHP bubble algorithm (recursive implementation), bubble recursion

Implementation

Copy code The code is as follows:

/*
Bubble algorithm (recursive implementation)
*/

function maoPao($array, $index=0)
{
$count = count($array);
If(($count-1) <= $index)
return $array;

for($i=$count-1; $i>$index; $i-- )
{
If($array[$i] < $array[$i-1])
           {
                $tmp = $array[$i];
$array[$i] = $array[$i-1];
               $array[$i-1] = $tmp;
}
}
$index++;
Return maoPao($array, $index);
//return maoPao($array, $index++);
}

$arr = array(12,4,3,1,9,5,6,8,7);
var_dump(maoPao($arr));

Result:

Copy code The code is as follows:

Array ( [0] => 1 [1] => 3 [2] => 4 [3] => 5 [4] => 6 [5] => 7 [6] => 8 [7] => 9 [8] => 12 )

Question:

I encountered a problem when trying this implementation, which has not yet been solved.
Here:

Copy code The code is as follows:

$index++;
return maoPao($array, $index);
//return maoPao($array, $index++);

/******************
If you use the third line directly instead of $index++ first, and then ruturn, you will enter an infinite loop. I output $index at the beginning of the function, both are 0, which means that the parameters passed to the recursive function after $index++ are not $index++ as they should be. The result (i.e. $index=$index+1).
Isn’t maoPao($array, $index++) a short way to write $index++; return maoPao($array, $index);? Why are the two results different? I hope you can get your answers.
******************/

Supplement:

Answer:

Copy code The code is as follows:

The difference between $index++ and ++$index is that $index++ is called the post-increment, and ++$index is called the pre-increment, although the final result of $index will always be +1. But there are differences when passing variables.

$index = 1;
$m = $index++;
echo $index.'
'; //The result is 2
echo $m.'
'; //The result is 1. Because it is a post-increment, the initial $index=1 will be assigned to $m first, and then $index will increase by 1;

$index = 1;
$n = ++$index;
echo $index.'
'; //The result is 2
echo $n; //The result is 2. Because it is a pre-increment, the operation of $index+1 will be performed first, and then assigned to $n;

This may not be easy to remember, so you must pay attention when using it. In the above question, I just ignored this problem, which caused $index to infinitely pass the value of 0 and cause the recursion to lock.